Chemical mechanical polishing apparatus with polishing pad including debris discharge tunnels and methods of operating the same

ABSTRACT

A polishing pad for chemical mechanical polishing (CMP) contains a lower polishing pad layer including a bottom surface of the polishing pad, an upper polishing pad layer including a top surface of the polishing pad, tunnels vertically spaced from the top surface of the polishing pad and from the bottom surface of the polishing pad, such that each of the tunnels laterally extends continuously to a respective opening in a peripheral sidewall of the polishing pad, and perforation holes vertically extending from the tunnels to the top surface of the polishing pad.

FIELD

The present disclosure relates generally to the field of semiconductor manufacturing, and specifically to a chemical mechanical polishing apparatus with a polishing pad including tunnels for discharge of debris and methods of operating the same.

BACKGROUND

Chemical mechanical polishing (CMP) is a process that forms smooth and planarized surfaces by removing protruding portions of a structure having topographic height variations. CMP is employed during semiconductor manufacturing to planarize top surfaces of patterned structures in semiconductor manufacturing. A CMP pad surface that is free of debris is desired to avoid formation of scratches on a polished surface during a CMP process.

SUMMARY

According to an aspect of the present disclosure, a polishing pad for chemical mechanical polishing (CMP) contains a lower polishing pad layer including a bottom surface of the polishing pad, an upper polishing pad layer including a top surface of the polishing pad, tunnels vertically spaced from the top surface of the polishing pad and from the bottom surface of the polishing pad, such that each of the tunnels laterally extends continuously to a respective opening in a peripheral sidewall of the polishing pad, and perforation holes vertically extending from the tunnels to the top surface of the polishing pad.

According to another aspect of the present disclosure, a CMP method includes chemically mechanically polishing a substrate on the polishing pad using a slurry, and flushing debris through the tunnels and out of the openings in the peripheral sidewall of the polishing pad that are connected to the tunnels.

According to yet another aspect of the present disclosure, a method of forming a polishing pad for chemical mechanical polishing (CMP) comprises providing an upper polishing pad layer, forming perforation holes from a top surface of the upper polishing pad layer toward a bottom surface of the upper polishing pad layer, forming grooves by patterning the bottom surface of the upper polishing pad layer, wherein each of the perforation holes is connected to a respective one of the grooves, and attaching the upper polishing pad layer to a lower polishing pad layer, wherein the grooves become tunnels that are bounded by portions of a planar surface of the lower polishing pad layer, and wherein each of the tunnels laterally extends continuously to a respective opening in a peripheral sidewall of the polishing pad.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a chemical mechanical polishing apparatus according to an embodiment of the present disclosure.

FIG. 2 is a vertical cross-sectional view of a wafer carrier within the CMP apparatus of FIG. 1 .

FIG. 3A is a top-down view of an upper polishing pad layer after formation of perforation holes according to an embodiment of the present disclosure.

FIG. 3B is a vertical cross-sectional view of the upper polishing pad layer along the vertical plane B-B′ of FIG. 3A.

FIG. 3C is a horizontal cross-sectional view of the upper polishing pad layer along the horizontal plane C-C′ of FIG. 3B.

FIG. 4A is a top-down view of the upper polishing pad layer after formation of grooves according to an embodiment of the present disclosure.

FIG. 4B is a vertical cross-sectional view of the upper polishing pad layer along the vertical plane B-B′ of FIG. 4A.

FIG. 4C is a horizontal cross-sectional view of the upper polishing pad layer along the horizontal plane C-C′ of FIG. 4B.

FIG. 5A is a top-down view of a polishing pad after attaching a lower polishing pad layer to the upper polishing pad layer according to an embodiment of the present disclosure.

FIG. 5B is a vertical cross-sectional view of the polishing pad along the vertical plane B-B′ of FIG. 5A.

FIG. 5C is a horizontal cross-sectional view of the polishing pad along the horizontal plane C-C′ of FIG. 5B.

FIG. 6A is a top-down view of an alternative configuration of a polishing pad after attaching a lower polishing pad layer to an upper polishing pad layer according to an embodiment of the present disclosure.

FIG. 6B is a vertical cross-sectional view of the polishing pad along the vertical plane B-B′ of FIG. 6A.

FIG. 6C is a horizontal cross-sectional view of the polishing pad along the horizontal plane C-C′ of FIG. 6B.

FIG. 7A is a horizontal cross-sectional of another alternative configuration of a polishing pad after attaching a lower polishing pad layer to an upper polishing pad layer according to an embodiment of the present disclosure.

FIG. 7B is a vertical cross-sectional view of the polishing pad along the vertical plane B-B′ of FIG. 7A.

FIG. 8 is a perspective view of a tunnel and a plurality of perforation holes attached to the tunnel according to an embodiment of the present disclosure.

FIG. 9 is a vertical cross-sectional view of the polishing pad of FIG. 7B during a water jet flushing step.

DETAILED DESCRIPTION

As discussed above, the embodiments of the present disclosure are directed to a chemical mechanical polishing apparatus with a polishing pad including tunnels for extraction of debris and methods of operating the same, the various aspects of which are described below.

In one embodiment, the polishing pad contains perforation holes and tunnels that are vertically spaced from the polishing surface. The tunnels are formed as buried laterally-extending cavities that extend to and are exposed at a sidewall (i.e., edge) of the polishing pad. The topmost surfaces of the tunnels are vertically spaced from the polishing surface of the polishing pad by a portion of the polishing pad including the perforation holes. The perforation holes are employed to collect debris from the work piece being polished and/or from the pad itself that is generated during the polishing operation. Additional debris may be generated when the polishing pad is sharpened with a diamond dresser in order to maintain the desired polishing rate. Cutting chips of the pad are generated and accumulated at the bottom of the grooves or holes in the polishing pad during the sharpening. When the accumulated polishing debris increases, it is released from the bottom of the grooves or holes and returned to the pad surface. The debris collected through the perforation holes can be flushed out through the tunnels, for example, by applying a water jet through the perforation holes and the tunnels, and flushing out the debris out through the ends of the tunnels in the peripheral sidewall of the polishing pad. Prompt removal of the various debris generated during the polishing helps prevent scratches on the polished surfaces of the work piece. The various aspects of the present disclosure are described with reference to accompanying drawings herebelow.

Referring to FIG. 1 , a chemical mechanical polishing (CMP) apparatus according to an embodiment of the present disclosure includes a polishing pad 112 located on a top surface of a platen 110, a wafer carrier 140 that is configured to hold a work piece (such as a substrate 41) upside down, a slurry dispenser 120 that is configured to dispense slurry 122 over the top surface of the polishing pad 112, and a pad conditioning unit (130, 132) that can be used to condition the top surface of the polishing pad 112.

The platen 110 can have a generally cylindrical shape, and can have a circular top surface that can be large enough to accommodate the polishing pad 112. The polishing pad 112 can have a generally circular horizontal-cross-sectional shape with a diameter that is at least twice the diameter of the substrate 41. For example, in embodiments in which the diameter of the substrate 41 is 300 mm, the diameter of the polishing pad 112 can be at least 600 mm. In embodiments in which the diameter of the substrate 41 is 450 mm, the diameter of the polishing pad 112 can be at least 900 mm. Generally, the ratio of the diameter of the polishing pad 112 to the diameter of the substrate 41 can be in a range from 2 to 6, such as from 2.5 to 4, although greater or lesser ratios can be used. The polishing pad 112 can include a textured top surface that is employed as a polishing surface during a polishing operation. The polishing pad 112 of the embodiments of the present disclosure includes debris 124 extraction tunnels connected to perforation holes in an upper polishing pad layer. Methods for manufacturing the polishing pad 112 of the present disclosure, and the structural features of the polishing pad 112 are described below in more detail with accompanying drawings.

The platen 110 can be configured to rotate around a vertical axis (VA) passing through the geometrical center of the platen 110. For example, a platen motor assembly 108 can be provided underneath the platen 110, and can rotate the platen 110 around the vertical axis (VA) passing through the geometrical center of the platen 110. As used herein, a geometrical center of an object refers to a center of mass of a hypothetical object occupying the same volume as the object and having a uniform density throughout. If an object has a uniform density, the geometrical center coincides with the center of gravity. The platen 110 can be configured to provide a rotational speed in a range from 10 revolutions per minute to 240 revolutions per minute, although faster or slower rotational speed can be used.

The wafer carrier 140 can be configured to hold the substrate 41 on a bottom surface thereof. Thus, the wafer carrier 140 can press the substrate 41 onto the top surface of the polishing pad 112. In one embodiment, the wafer carrier 140 can include a vacuum chuck configured to provide suction to the backside of the substrate 41. In one embodiment, differential suction pressures can be applied across different backside areas of the substrate 41. For example, the suction pressure applied to the center portion of the substrate 41 can be different from the suction pressure applied to the peripheral portion of the substrate 41 to provide uniform polishing rate across the entire area of the front side of the substrate 41 that contacts the polishing pad 112. In one embodiment, the wafer carrier 140 can include a retaining ring having an annular shape and configured to hold the substrate 41 therein so that the substrate 41 does not slide out from underneath the wafer carrier 140.

A polishing head 142 can be provided over the wafer carrier 140. The polishing head 142 can include a rotation mechanism that provides rotation to the wafer carrier 140. In some embodiments, a gimbal mechanism can be provided between the rotation mechanism and the wafer carrier 140 so that the wafer carrier 140 tilts in a manner that provides maximum physical contact between the entire front surface of the substrate 41 and the polishing pad 112. The combination of the polishing head 142 and the wafer carrier 140 constitutes a wafer polishing unit (140, 142) that positions and rotates the substrate 41 in a manner that induces polishing of material portions on the front side of the substrate 41 through abrasion caused by sliding contact with the top surface of the polishing pad 112.

In one embodiment, the substrate 41 and the wafer carrier 140 can rotate around the vertical axis (not illustrated) passing through the geometrical center of the wafer carrier 140. A polishing pivot pillar structure 144 can be affixed to a frame (not shown) of the CMP apparatus such that the polishing pivot pillar structure 144 can rotate around a vertical axis (not illustrated) passing through the geometrical center of the polishing pivot pillar structure 144. The vertical axis passing through the geometrical center of the polishing pivot pillar structure 144 can be stationary relative to the frame of the CMP apparatus.

A polishing arm 146 mechanically connects the polishing head 142 to the polishing pivot pillar structure 144. Thus, upon rotation of the polishing pivot pillar structure 144 around the vertical axis passing through the geometrical center of the polishing pivot pillar structure 144, the polishing arm 146 can rotate around the vertical axis passing through the geometrical center of the polishing pivot pillar structure 144. The polishing head 142 can move around the vertical axis passing through the geometrical center of the polishing pivot pillar structure 144 over the polishing pad 112. Lateral movement of the wafer polishing unit (140, 142) over the polishing pad 112 can enhance uniformity of polish rate across the substrate 41 during the CMP process.

The slurry dispenser 120 can be configured to dispense the slurry 122 over the top surface of the polishing pad 112. The slurry 122 can include any slurry known in the art, such as commercially available slurries for chemical mechanical polishing processes.

The pad conditioning unit (130, 132) can be used to precondition the polishing pad 112 prior to and/or during the CMP process that is used to polish material portions from the front surface of the substrate 41 that contacts the top surface of the polishing pad 112. In one embodiment, the pad conditioning unit (130, 132) can include a pad conditioning disk 130 and a conditioning head 132 that is configured to hold the pad conditioning disk 130. The pad conditioning disk 130 includes an abrasive bottom surface that can precondition the top surface of the polishing pad 112. Typically, the abrasive bottom surface of the pad conditioning disk 130 embeds abrasive particles, such as diamond particles. The pad conditioning disk 130 can be attached to the conditioning head 132 in a manner that provides rotation of the pad conditioning disk around a vertical axis (not shown) passing through the geometrical center of the pad conditioning disk 130 without falling out from the conditioning head 132.

A conditioner pivot pillar structure 134 can be affixed to a frame (not shown) of the CMP apparatus such that the conditioner pivot pillar structure 134 can rotate around a vertical axis (not shown) passing through the geometrical center of the conditioner pivot pillar structure 134. The vertical axis passing through the geometrical center of the conditioner pivot pillar structure 134 can be stationary relative to the frame of the CMP apparatus.

A pad conditioner arm 136 mechanically connects the conditioning head 132 to the conditioner pivot pillar structure 134. A pad conditioner arm 136 mechanically connects the conditioning head 132 to the conditioner pivot pillar structure 134. Thus, upon rotation of the conditioner pivot pillar structure 134 around the vertical axis passing through the geometrical center of the conditioner pivot pillar structure 134, the pad conditioner arm 136 can rotate around the vertical axis passing through the geometrical center of the conditioner pivot pillar structure 134. The conditioning head 132 can move around the vertical axis passing through the geometrical center of the conditioner pivot pillar structure 134 over the polishing pad 112. Lateral movement of the pad conditioning unit (130, 132) over the polishing pad 112 can enhance uniformity of the surface condition of the polishing pad 112 after the pad pre-conditioning process.

The CMP apparatus of the embodiments of the present disclosure can include a process controller 200 electrically connected (e.g., via wired and/or wireless connections) to electrical components that control movement of various mechanical parts of the CMP apparatus. For example, the process controller 200 can be electrically connected to, and can be configured to control operation of, each of the platen motor assembly 108, the polishing pivot pillar structure 144, the wafer polishing unit (140, 142), the conditioner pivot pillar structure 134, the pad conditioning unit (130, 132), and the slurry dispenser 120. For example, the process controller 200 can control the rotational speed of the platen 110, the polishing pivot pillar structure 144, the wafer carrier 140, the conditioner pivot pillar structure 134, and the pad conditioning disk 130, and can control the location of the slurry dispensation point and the rate of slurry dispensation.

Generally, the CMP apparatus according to various embodiments can include a polishing pad 112 located on a top surface of a platen 110 configured to rotate around a vertical axis VA passing through the platen 110, a wafer carrier 140 that holds a substrate 41 and facing the polishing pad 112, a slurry dispenser 120 configured to dispense slurry 122 over the polishing pad 112, and a process controller 200 configured to control operation of components within the wafer carrier 140 and other components of the CMP apparatus. For example, the process controller 200 may control the rotation speed of the platen 110, the rotation speed of the wafer carrier 140, and/or the downforce that the wafer carrier 140 applies to the polishing pad 112. The CMP apparatus may include an assembly of a conditioning head 132 and a pad conditioning disk 130 that is configured to condition the top surface of the polishing pad 112.

Referring to FIG. 2 , a wafer carrier 140 is illustrated in a state in which a substrate 41 is located into the wafer carrier 140. The wafer carrier 140 comprises a backside plate 403 configured to press the substrate 41 onto a top surface of the polishing pad 112, and a wafer carrier frame 401 that holds the backside plate 403 with a cavity 409 between a top surface (i.e., a backside surface) of the backside plate 403 and an inner surface of the wafer carrier frame 401. In one embodiment, the wafer carrier frame 401 comprises a tubular portion (i.e., a hollow cylindrical portion) and a top plate portion adjoined to a top periphery of the tubular portion. The backside plate 403 can be configured to press the substrate 41 toward the polishing pad 112 such that a predominant fraction of the bottom surface portion of the substrate 41 can be flush with a polishing surface PS, which is located in a horizontal plane including an annular bottom surface of the tubular portion of the wafer carrier frame 401. A predominant fraction refers to a fraction that is at least 50% of an entirety. The cavity 409 can be provided between the top surface of the backside plate 403 and a bottom surface of the top plate portion of the wafer carrier frame 401, and can be laterally surrounded by the tubular portion of the wafer carrier frame 401.

The polishing pad 112 of the embodiments present disclosure can be formed by the process to be described below.

Referring to FIGS. 3A-3C, an upper polishing pad layer 320 can be provided as a circular disk having a uniform thickness throughout. The upper polishing pad layer 320 is a component layer for a polishing pad 112 to be formed and mounted on a top surface of a platen 110 to provide the CMP apparatus illustrated in FIG. 1 . The upper polishing pad layer 320 may be free of any pattern at this processing step.

The upper polishing pad layer 320 may be formed from a polymer, such as polyurethane. The thickness of the upper polishing pad layer 320 may be in a range from 0.7 mm to 3 mm, although lesser and greater thicknesses may also be employed.

According to an aspect of the present disclosure, perforation holes 13 can be formed into the upper polishing pad layer 320. In one embodiment, the perforation holes 13 may be formed from a top surface of the upper polishing pad layer 320 toward a bottom surface of the upper polishing pad layer 320, and the depth of the perforation holes 13 may be at least 10% of the thickness of the upper polishing pad layer 320. In one embodiment, the depth of the perforation holes 13 may be in a range from 10% to 99% of the thickness of the upper polishing pad layer 320. Alternatively, the perforation holes 13 may extend through the entire thickness of the upper polishing pad layer 320. In this case, the perforation holes 13 may be formed from the top surface of the upper polishing pad layer 320. Toward the bottom surface of the upper polishing pad layer 320, or from the bottom surface of the upper polishing pad layer 320 to the top surface of the upper polishing pad layer 320.

Each of the perforation holes 13 may have a cylindrical shape. The diameter of each perforation hole 13 may be in a range from 0.2 mm to 2 mm, such as from 0.4 mm to 1 mm, although lesser and greater diameters may also be employed. Other hole 13 shapes besides cylindrical may also be used.

According to one aspect of the present disclosure, the perforation holes 13 may be formed along a pattern of a grid, such as a rectangular grid or a square grid. Thus, multiple rows of perforation holes 13 may be formed into the upper polishing pad layer 320 such that each row of perforation holes 13 comprises a plurality of perforation holes 13 that are arranged along a first horizontal direction, and the multiple rows of perforation holes 13 are laterally spaced apart along a second horizontal direction that is perpendicular to the first horizontal direction.

In one embodiment, the perforation holes 13 may be formed as a rectangular periodic array having a first periodicity along the first horizontal direction and having a second periodicity along the second horizontal direction. The first periodicity (i.e., a first pitch) may be in a range from 5 times the diameter of each perforation hole 13 to 1,000 times the diameter of each perforation hole 13, and/or in a range from 20 times the diameter of each perforation hole 13 to 100 times the diameter of each perforation hole 13. Likewise, the second periodicity (i.e., a second pitch) may be in a range from 5 times the diameter of each perforation hole 13 to 1,000 times the diameter of each perforation hole 13, and/or in a range from 20 times the diameter of each perforation hole 13 to 100 times the diameter of each perforation hole 13.

Referring to FIGS. 4A-4C, grooves 17′ can be formed on the backside of the upper polishing pad layer 320. The grooves 17′ can be formed as straight or curved trenches laterally extending along the first horizontal direction or along the second horizontal direction such that they reach the edge of the upper polishing pad layer 320. According to an embodiment of the present disclosure, the depth of the grooves 17′ may be in a range from 20% to 80% of the thickness of the upper polishing pad layer 320, such as from 30% to 70% of the thickness of the upper polishing pad layer 320. Each groove 17′ can be formed below a respective row of perforation holes 13 such that each perforation hole 13 within the row of perforation holes 13 is connected to the respective groove 17′. In one embodiment, each perforation hole 13 can be connected to a respective one of the grooves 17′.

In one non-limiting aspect of the present disclosure, the grooves 17′ may have a uniform depth and/or a uniform width. Alternatively, the grooves 17′ may have a non-uniform depth and/or a non-uniform width. The width of each groove 17′ can be greater than the diameter of each perforation hole 13. For example, the uniform width of each groove 17′ may be in a range from 0.3 mm to 3 mm, such as from 0.6 mm to 1.5 mm, although lesser and greater widths can also be employed. The periodicity of the grooves 17′ can be the same as the periodicity within the rectangular array of perforation holes 17. Thus, the grooves 17′ can be formed as a two-dimensional periodic array of grooves laterally extending along the first horizontal direction or along the second horizontal direction, and the perforation holes 13 may be located at cross-points of the grooves 17′, i.e., at points at which a first groove 17′ laterally extending along the first horizontal direction intersects a second groove 17′ laterally extending along the second horizontal direction. Each of the grooves 17′ extends to a peripheral sidewall of the upper polishing pad layer 320 such that an opening is formed at each end of a groove 17′ located at the periphery of the upper polishing pad layer 320.

Generally, the grooves 17′ can be formed by patterning the bottom surface of the upper polishing pad layer 320. Each of the perforation holes 13 can be connected to a respective one of the grooves 17′. Each of the grooves 17′ laterally extends continuously to a peripheral sidewall (i.e., to the edge) of the upper polishing pad layer 320. Openings 19 connected to a respective one of the grooves 17′ can be formed in the peripheral sidewall of the upper polishing pad layer 320.

In one embodiment, the grooves 17′ are arranged as a network in which a first subset of the grooves 17′ that laterally extend along a first horizontal direction intersects a second subset of the grooves 17′ that laterally extend along a second horizontal direction that is different from the first horizontal direction. In one embodiment, the second horizontal direction can be perpendicular to the first horizontal direction.

The grooves 17′ are vertically spaced from the top surface of the upper polishing pad layer 320 by a portion of the upper polishing pad layer 320 that contains the perforation holes 13 therein. The portion of the upper polishing pad layer 320 located between the top surface of the upper polishing pad layer 320 and the horizontal plane including the horizontal surfaces of the grooves 17′ is herein referred to as a hole-containing pad sub-layer 32A of the upper polishing pad layer 320. The portion of the upper polishing pad layer 320 that contains the grooves 17′ and located between a horizontal plane including the bottom surface of the upper polishing pad layer 320 and the horizontal plane including the horizontal surfaces of the grooves 17′ is herein referred to as a groove-containing pad sub-layer 32B of the upper polishing pad layer 320. As used herein, a “sub-layer” refers to a component of a layer.

During usage of the polishing pad 112, which includes upper polishing pad layer 320, the perforation holes 13 provide vertical paths for movement of debris, and the grooves 17′ provide horizontal paths for movement of debris. The bottom end of each of the perforation holes 13 is connected to at least one groove 17′, such as a pair of grooves 17′, to facilitate transport of debris during subsequent usage of the polishing pad 112. The grooves 17′ are vertically spaced from the top surface of the upper polishing pad layer 320 by a vertical distance, which can be the same as the thickness of the hole-containing pad sub-layer 32A.

Referring to FIGS. 5A-5C, a lower polishing pad layer 323 can be provided. The lower polishing pad layer 323 can have the same size (e.g., the same diameter) as the upper polishing pad layer 320. In one embodiment, the lower polishing pad layer 323 may comprise a nonwoven fabric, which may, or may not, be impregnated with a polymer, such as polyurethane. The lower polishing pad layer 323 may have a uniform thickness throughout, which may be in a range from 0.5 mm to 2 mm, such as from 0.7 mm to 1 mm, although lesser and greater thicknesses may also be employed.

According to an embodiment of the present disclosure, an adhesive layer 324 can be applied to the top surface of the lower polishing pad layer 323 and/or to the bottom surface of the upper polishing pad layer 320 (i.e., on the side of the grooves 17′). The lower polishing pad layer 323 can be attached to the upper polishing pad layer 320 within the adhesive layer 324 therebetween, or the upper polishing pad layer 320 can be attached to the lower polishing pad layer 323 with the adhesive layer 324 therebetween. Upon optional curing of the adhesive layer 314, the polishing pad 112 is formed. The polishing pad 112 can be subsequently mounted onto the platen 110 in the CMP apparatus of FIG. 1 .

Upon attaching the upper polishing pad layer 320 to the lower polishing pad layer 323, the grooves become tunnels 17 that are bounded by portions of a planar surface of the lower polishing pad layer 323. Thus, the polishing pad 112, as mounded on the platen 110, comprises tunnels 17 vertically spaced from a top surface of the polishing pad 112 and from a bottom surface of the polishing pad 112. Further, the polishing pad 112 comprises perforation holes vertically extending from the tunnels 17 to the top surface of the polishing pad 112.

In one embodiment, each of the tunnels 17 laterally extends continuously to a respective opening in a peripheral sidewall (i.e., edge) of the polishing pad 112. In one embodiment, the tunnels 17 are arranged as a network in which a first subset of the tunnels 17 that laterally extend along a first horizontal direction intersects a second subset of the tunnels 17 that laterally extend along a second horizontal direction that is different from the first horizontal direction. The second horizontal direction can be perpendicular to the first horizontal direction. In one embodiment, the perforation holes 13 are arranged as a rectangular array of perforation holes 13, and each of the perforation holes 13 is connected to a cross-point of a respective tunnel 17 in the first subset of the tunnels 17 and a respective tunnel 17 in the second subset of the tunnels 17. In one embodiment, each of the tunnels 17 has a uniform height and a uniform width.

Referring to FIGS. 6A-6C, an alternative configuration of a polishing pad 112 is illustrated after attaching a lower polishing pad layer 323 to an upper polishing pad layer 320. In the alternative configuration, the pattern of the perforation holes 13 may be a radial pattern, i.e., a pattern arranged along a horizontal direction along a line passing through a geometrical center of the polishing pad 112. The pattern of the grooves 17′ formed at a processing step corresponding to a processing step of FIGS. 4A-4C can also be a radial pattern. In one embodiment, the grooves 17′ can be arranged in a radial pattern such that each path from a point within the grooves 17′ to the respective opening in the peripheral sidewall comprises a segment, such as a straight segment, that extends along a radial direction from a geometrical center of the upper polishing pad layer 320. In other words, each of the grooves 17′ can be formed along a horizontal direction that passes through the geometrical center of the polishing pad 112. The grooves 17′ can be formed such that each of the perforation holes 13 is connected to a respective one of the grooves 17′.

Upon attaching the lower polishing pad layer 323 to the upper polishing pad layer 320, each of the tunnels 17 can laterally extend continuously to a respective opening in a peripheral sidewall of the polishing pad 112. In one embodiment, the tunnels 17 can be arranged in a radial pattern such that each path from a point within the tunnels 17 to the respective opening in the peripheral sidewall comprises a segment, such as a straight segment, that extends along a radial direction from a geometrical center of the polishing pad 112.

In another alternative embodiment shown in FIGS. 7A and 7B, the segments may be curved, such that the tunnels 17 have a curved horizontal shape, such as a spiral shape that extends from the center of the polishing pad 112.

In one embodiment, at least a subset, and/or the entirety, of the perforation holes 13 can be arranged as rows of perforation holes that are arranged along a respective radial direction and connected to a respective one of the tunnels 17. In one embodiment, each of the tunnels 17 has a uniform height and/or a uniform width. In another embodiment, each of the tunnels 17 has a non-uniform height and/or a non-uniform width.

Referring to FIG. 8 , a perspective view of a tunnel 17 and a plurality of perforation holes 13 connected (i.e., fluidly connected) to the tunnel 17 is shown. The perforation holes 13 do not extend to the backside surface of the polishing pad 112. Thus, the backside surface of the polishing pad 112 can be free of any hole.

Generally, all or a subset of the perforation holes 13 can be fluidly connected to the tunnels 17 such that a fluid can flow between the perforation hole 13 and the fluidly connected tunnel 17. In some embodiments, all perforation holes 13 are connected to at least one tunnel 17. In an alternative embodiment, some of the perforation holes 13 are connected to at least one tunnel 17 and the remaining perforation holes 13 are not connected to any tunnels 17. In the alternative embodiment, the remaining perforation holes 13 which are not connected to any tunnels 17 are used as polishing slurry storage reservoirs. In one embodiment, the perforation holes 13 have a respective cylindrical shape having a diameter, and the tunnels 17 have a respective uniform width that is greater than the diameter.

After mounting the polishing pad 112 onto the platen 110 as illustrated in FIG. 1 , the wafer carrier 140 and a slurry dispenser 120 can be positioned over the polishing pad 112, and a chemical mechanical polishing operation can be performed. As discussed above, the wafer carrier 140 can be configured to hold a substrate 41, and the slurry dispenser 120 can be configured dispense slurry 122 over the polishing pad 112. The CMP debris 124 is flushed through the tunnels 17 and out of openings 19 in a peripheral sidewall of the polishing pad 112 that are connected to the tunnels 17.

Referring to all drawings and according to various embodiments of the present disclosure, a polishing pad 112 for chemical mechanical polishing (CMP) contains a lower polishing pad layer 323 including a bottom surface of the polishing pad, an upper polishing pad layer 320 including a top surface of the polishing pad, tunnels 17 vertically spaced from the top surface of the polishing pad and from the bottom surface of the polishing pad, such that each of the tunnels 17 laterally extends continuously to a respective opening 19 in a peripheral sidewall of the polishing pad 112, and perforation holes 13 vertically extending from the tunnels 17 to the top surface of the polishing pad 112.

In one embodiment, the lower polishing pad layer 323 is attached to the upper polishing pad layer 320 by an adhesive layer 324. In one embodiment, the upper polishing pad layer 320 and the lower polishing pad layer 323 comprise different materials, such as polyurethane and non-woven material, respectively. In one embodiment, the upper polishing pad layer 320 vertically extends from the horizontal plane to the top surface of the polishing pad 112.

The CMP apparatus of FIG. 1 can be employed to polish a substrate containing an in-process semiconductor device, as shown in FIG. 9 . When the surface roughness of the top surface of the polishing pad 112 decreases to a level that requires re-conditioning, the top surface of the polishing pad 112 can be sharpened (i.e., roughened) with a dresser, such as a diamond dresser. Debris 124 from the top surface of the polishing pad 112 fall through the perforation holes 13 into the tunnels 17 during the surface re-conditioning process and/or during the CMP process. To facilitate removal of debris, a flow of a cleaning liquid 352 is provided from a cleaning fluid dispenser 350 through the perforation holes 13 and through the tunnels 17. The debris 124 is flushed through the tunnels 17 and out of openings 19 in a peripheral sidewall of the polishing pad 112 that are connected to the tunnels 17. In one embodiment, the cleaning liquid comprises water, and the flow of the cleaning liquid may be provided by applying a water jet from a dispenser 352 which comprises a water nozzle located above the polishing pad 112 toward the perforation holes 13.

Upon repeatedly sharpening the polishing pad 112 with a dresser, the height of the perforation holes 13 is reduced, and the flow of debris 124 through the perforation holes 13 into the tunnels becomes easier. Thus, the polishing pad 112 of the embodiments of the present disclosure permits removal of accumulated debris (which may induce scratches on polished surfaces of processed substrates 41 if not removed) through the perforation holes 13 and the tunnels 17.

In addition, scratch sources, such as CMP debris 124 can flow into the perforation holes 13 during the polishing operation, and can flow outward through the tunnels 17 during the polishing operations. Thus, the CMP apparatus of the embodiments of present disclosure can reduce scratches on the polished surfaces of processed substrates 41. During operation of the CMP apparatus, the slurry 122 and debris 124 can be continuously removed through the perforation holes 13 and the tunnels 17 in the polishing pad 112. The increased removal rate for the slurry 122 can be compensated by increasing the slurry supply rate.

Since the total surface area of the polishing pad 112 is about the same as the total surface area of a conventional polishing pad (except for the reduction of the areas due to the presence of the perforation holes 13), adjustment to the processing parameters (such as the downforce applied by the wafer carrier 140) can be minimal. Scratch sources (e.g., debris 124) that fall into the perforation holes 13 and accumulate at the bottom of the perforation holes 13 and within the tunnels 17 can be removed during a separate flushing process and/or during the polishing process while maintaining the contact area between the substrate 41 being polished and the polishing pad 112 during the polishing operation.

Although the foregoing refers to particular preferred embodiments, it will be understood that the disclosure is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the disclosure. Where an embodiment employing a particular structure and/or configuration is illustrated in the present disclosure, it is understood that the present disclosure may be practiced with any other compatible structures and/or configurations that are functionally equivalent provided that such substitutions are not explicitly forbidden or otherwise known to be impossible to one of ordinary skill in the art. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety. 

What is claimed is:
 1. A polishing pad for chemical mechanical polishing (CMP), comprising: a lower polishing pad layer comprising a bottom surface of the polishing pad; an upper polishing pad layer comprising a top surface of the polishing pad; tunnels vertically spaced from the top surface of the polishing pad and from the bottom surface of the polishing pad, wherein each of the tunnels laterally extends continuously to a respective opening in a peripheral sidewall of the polishing pad; and perforation holes vertically extending from the tunnels to the top surface of the polishing pad.
 2. The polishing pad of claim 1, wherein the tunnels are arranged in a radial pattern such that each path from a point within the tunnels to the respective opening in the peripheral sidewall comprises a segment that extends along a radial direction from a geometrical center of the polishing pad.
 3. The polishing pad of claim 2, wherein a subset of the perforation holes is arranged as rows of perforation holes that are arranged along a respective radial direction and connected to a respective one of the tunnels.
 4. The polishing pad of claim 1, wherein the tunnels are arranged in a spiral pattern.
 5. The polishing pad of claim 1, wherein the tunnels are arranged as a network in which a first subset of the tunnels that laterally extend along a first horizontal direction intersects a second subset of the tunnels that laterally extend along a second horizontal direction that is different from the first horizontal direction.
 6. The polishing pad of claim 5, wherein the second horizontal direction is perpendicular to the first horizontal direction.
 7. The polishing pad of claim 5, wherein: the perforation holes are arranged as a rectangular array of perforation holes; and each of the perforation holes is connected to a cross-point of a respective tunnel in the first subset of the tunnels and a respective tunnel in the second subset of the tunnels.
 8. The polishing pad of claim 1, wherein each of the tunnels has a uniform height and a uniform width.
 9. The polishing pad of claim 1, wherein the perforation holes and the tunnels are located in the upper polishing pad layer.
 10. The polishing pad of claim 9, further comprising an adhesive layer located between the upper and the lower polishing pad layers, wherein the lower polishing pad layer is attached to the upper polishing pad layer by the adhesive layer.
 11. The polishing pad of claim 9, wherein the upper polishing pad layer and the lower polishing pad layer comprise different materials.
 12. The polishing pad of claim 9, wherein the upper polishing pad layer comprises polyurethane, and the lower polishing pad layer comprises a non-woven material.
 13. The polishing pad of claim 1, wherein: the perforation holes have a respective cylindrical shape having a diameter; and the tunnels have a respective uniform width that is greater than the diameter of the perforation holes.
 14. A CMP apparatus, comprising: a platen; the polishing pad of claim 1 located on a top surface of the platen; a wafer carrier configured to hold a substrate and facing the polishing pad; and a slurry dispenser configured dispense a slurry over the top surface of the polishing pad.
 15. A method of operating the CMP apparatus of claim 14, comprising: chemically mechanically polishing a substrate on the polishing pad using the slurry; and flushing debris through the tunnels and out of the openings in the peripheral sidewall of the polishing pad that are connected to the tunnels.
 16. The method of claim 15, wherein flushing the debris comprises applying a water jet from above the polishing pad toward the perforation holes.
 17. A method of forming a polishing pad for chemical mechanical polishing (CMP), comprising: providing an upper polishing pad layer; forming perforation holes from a top surface of the upper polishing pad layer toward a bottom surface of the upper polishing pad layer; forming grooves by patterning the bottom surface of the upper polishing pad layer, wherein each of the perforation holes is connected to a respective one of the grooves; and attaching the upper polishing pad layer to a lower polishing pad layer, wherein the grooves become tunnels that are bounded by portions of a planar surface of the lower polishing pad layer, and wherein each of the tunnels laterally extends continuously to a respective opening in a peripheral sidewall of the polishing pad.
 18. The method of claim 17, the grooves are arranged in a spiral pattern.
 19. The method of claim 17, wherein the grooves are arranged in a radial pattern such that each path from a point within the grooves to the respective opening in the peripheral sidewall comprises a segment that extends along a radial direction from a geometrical center of the upper polishing pad layer.
 20. The method of claim 17, wherein the grooves are arranged as a network in which a first subset of the grooves that laterally extend along a first horizontal direction intersects a second subset of the grooves that laterally extend along a second horizontal direction that is different from the first horizontal direction. 